1. Field of the Invention
The present invention relates to a low NOx burner and a method of controlling recirculation of exhaust gas, and more particularly to a low NOx burner for use in a combustion apparatus for an absorption type refrigeration machine, a steam boiler, a hot water boiler, a heat cooking machine, a heater and another unit and a method of controlling recirculation of exhaust gas, which is capable of synchronizing with change in the load if the load is changed, stably maintaining the state of combustion and restraining the quantity of generation of NOx.
2. Background Art
Recently, required emission levels of NOx have been regulated severely such that (1) NOx must be 40 ppm (O.sub.2 =0%) or lower in cold regions, (2) that from gas fuel except 13A must be 60 ppm or lower and (3) that from oil fuel must be 60 ppm or lower.
Hitherto, low NOx burners of a type arranged to be operated by a method of recirculating exhaust gas have been widely used, in which an exhaust gas recirculating duct 7a is, as shown in FIG. 3, provided, which has an end connected to a position near an exhaust gas box 8 and another end connected to an air suction passage 9 for an electric fan F to circulate and supply combustion gas so as to lower the temperature of flames of a burner body 1c in order to restrict generation of NOx (refer to Japanese Utility-Model Laid-Open No. 2-7414 and so forth). Referring to FIG. 3, reference numeral 2 represents a fuel supply passage, 3 represents a nozzle, 4 represents a passage for supplying air for combustion, 5 represents a burner port, 6 represents a combustion chamber and 10 represents a gas duct.
However, the above-mentioned conventional method structured such that the air suction passage 9 and the exhaust gas box 8 are connected to each other by the exhaust gas recirculating duct 7a so as to attract a portion of the combustion gas into the air suction passage 9 through the gas recirculating duct 7a has the problems below: the quantity of recirculation can easily considerably be changed attributable to change in the draft pressure in the exhaust gas box 8 and the combustion chamber 10 and the balance between the air supply and gas exhaustion. As a result, the quantity of recirculation of the exhaust gas cannot be controlled to a predetermined quantity, thus resulting in that the combustion state becomes unstable. Moreover, the temperature of the flames of the burner body 1c is changed considerably, thus raising a problem in that the quantity of NOx which will be generated becomes unstable. Since the combustion gas, which is recirculated, is introduced into the exhaust gas recirculating duct 7a which has been cooled, the combustion gas is condensed on the inner surface of the recirculating duct 7a. Thus, there arises a problem in that, for example, the exhaust gas recirculating duct 7a is rusted and therefore the durability of the same deteriorates.